Process of making cellulose xanthate solutions



' sired solution of cellulose xanthate.

Patented May 10, 1938 airwas PATENT OFFICE PROCESS OF MAKING CELLULOSEXAN- THATE SOLUTIONS George A. Richter, Berlin, N. 11., assignor toBrown Company, Berlin, N. IL, a corporation of Maine No Drawing.Application February 1987, Serial No. 123,850 a 4 Claims.

This invention relates to a process of making cellulose xanthatesolutions and more particularly to a process involving the mixture andreaction of cellulose fiber, an aqueous solution-of caustic soda, andliquid carbon bisulphide to produce in a continuous operation in asingle vessel cellulose xanthate solutions or viscose syrupssuch as areuseful in the'manufacture of artificial silk, films, or kindred ultimateproducts by the usual practices.

In my application Serial No. 58,539, filed January 10, 1936, I havedescribed a so-called oneatep xanthating operation involving the use asraw material of chips or fragments of sheeted cellulose fiber orpulpboard, the placement of such chips or fragments in a closed mixingand reacting vessel, the mixing of caustic soda solution with the chargeof chips or fragments in the vessel until they are successivelythoroughly soaked and disintegrated to form a fiber suspension in thesolution substantially free from fiber aggregates or clumps, and themixing of liquid carbon bisulphide with the fiber suspension in thevessel until the fiber is substantially completely xanthated anddissolved to yield the de- In accordance with the present invention,once the mass of sheet fragments or pulpboard chips has been confined inthe closed mixing vessel, air is evacuated from the vessel to deaerateto a large extent I the chips or fiber aggregatesand thus to induce morerapid penetration of the subsequently added caustic soda solution intoand throughout the chips and, as mixing of the solution with the chipsis effected, the defiberizatlon or disintegration of the chips to form afiber suspension of the desired freedom from clumps or fiber aggregates.The deaeration of the charge .of pulpboard chips or fiber aggregatesprior to the addition of the caustic soda solution is of considerableimportance in that the rate of penetration of caustic soda solution intothe chips otherwise depends upon such factors as the compactness,texture, size of interstices, and moisture content of the sheets orboards from which the chips are de rived. In this connection, it mightbe observed that the volume of caustic soda solution added to the vesselis calculated to produce a finished viscose solution of .a particularcausticity with- "out need of draining excess solution from the vessel.Because such a volume ofsolution is insufllcient to submerge or coverthe wood pulp chips completely, there is less tendency to displace orexpel air from the chip interstices than when anexcessive volume ofsolution is employed.

By deaerating the chips and thus doing away with the indeterminate,relatively slow displacement of air from the chips by the caustic sodasolution, the efiects of variations in the characteristics of the sheetsor boards from which the chips are derivedare minimized and it becomespossible to shorten appreciably the period for the soaking anddisintegration of the chips, to foster a more uniform and completepenetration of the chips throughout, and at the same time to produce afiber suspension in caustic soda solution of the desired smoothness orfreedom from fiber aggregates. Thus, by the practice of the presentinvention, it is possible to save a half an hour or more in the processas a whole when using pulpboard chips as-raw material and thus torealize an increased production of the desired quality of cellulosexanthate solution from a reaction vessel of given size or capacity.

- In practicing the present invention, sheets or boards composed ofvarious kinds of wood pulp or other cellulose fiber may be cut intopieces or chips of the small size desired for introduction into themixing and reacting vessel, as described in my application Serial No.58,539. Thus, pulpboard produced from substantially unbeaten wood pulpand having a compactness or density varying from about 50 to and athickness ranging from 0.030 to 0.060 inch may be cut into chips 01,say, about square to 1" square, and the chips 'added to a mixing andreacting vessel of any suitable type, for instance, that disclosed inapplication Serial No. 53,689, filed December 10, 1935, by

Orton B. Brown. The sheet compactness values mentioned are obtained bydividing the basis weight of the sheet in pounds by its thickness ininches and multiplying by the factor 10 The basis weight signifies theweight in pounds of 480 sheets whose dimensions are 24 x 36 inches,

that is, the weight of 2880 square feet of sheet material.

After the vessel has been partially filled with a mass .of the pulpchips, it is closed and placed under the evacuating action of a vacuumpump until a comparatively high degree of vacuum or sub-atmosphericpressure is attained in the vessel, for instance, an absolute pressureof 1 to 5 pounds, in consequence of which the chips are very largelydeaerated. In the case of a vessel whose mixing blades are constructedto permit a heating medium to be circulated therethrough, as is true ofthe apparatus of application Serial No. 53,689, it is advantageous totumble or revolve the vessel while it is being evacuated and whilea 5heating medium is being circulated through its idle mixing blades so asto raise the temperature of the pulp chips to, say, 50 C. and thus toexpel air from the chip interstices as well as residual moisture such ascauses dilution of the caustic soda solution subsequently added to thechips. When the desired degree of vacuum has been created in the vessel,communication between the vessel and the vacuum pump is cut off andcaustic soda solution in desired volume and concentration is injectedinto the closed, deaerated vessel. The caustic soda solution is quicklyand substantially uniformly absorbed by the mass of deaerated chips andby the fibrous structure of the individual chips so that upon operatingthe vessel and its mixing blades for a comparatively short period oftime, the chips, as they are mixed with the solution, are softened,swollen, and finally disintegrated to yield a thick or quasiplasticsuspension of fibers in caustic soda solution of the desired smoothnessor freedom from fiber aggregates realized. Liquid carbon bisulphide inthe desired volume may then be injected into the vessel and mixingaction in the vessel continued until the fibers in suspension have beensubstantially completely xanthated and dissolved to yield a solution ofcellulose xanthate or viscose syrup of the desired character. The entireoperation is carried out with the vessel only partially filled, 'thatis, with an empty space above the vessel contents.

In some instances, after the deaerated chips or sheet fragments havebeen thoroughly soaked and softened with the caustic soda solution andfinally resolved or disintegrated into the desired suspensionsubstantially devoid of fiber aggregates, a suitable gas may beintroduced into the empty space of the vessel above the fibersuspension. Thus, while the smooth or salve-like suspension is beingmixed or churned and before the liquid carbon bisulphide is added,oxygen may be introduced into the vessel and mixing or churning of thesuspension continued. Such oxygenation of the suspension, particularlyunder superatmospheric oxygen pressures, causes reduction in thesolution viscosity of the cellulose and promotes its subsequentxanthation by the liquid carbon bisulphide. fiber is of sufficiently lowviscosity to begin with and there is no need for or advantage inreducing its viscosity by oxygenatiomit may be desirable to introduceinto the vessel above the suspension an inert or non-oxidizing gas suchas nitrogen under ordinary or superatmospheric pressures moreparticularly for the purpose of precluding possible ignition of theliquid carbon bisulphide subsequently added to the vessel and avoidingchange in the viscosity or other characteristics of the cellulosethrough leakage of air into the vessel. In other substances, afteroxygenation of the suspension has been effected for the desired periodof time so as to reduce the viscosity of the fiber, the oxygen may beevacuated or removed from the gas space in the vessel and replaced by.nitrogen so as to provide an inert atmosphere in When the cellulose 10%each is desired, the procedure hereof, so far as concernsproportionality of the various" rcacting ingredients and the temperatureconditions under which xanthation is performed, may advantageouslyaccord with the disclosure of my application Serial No. 58,539. It ispossible, however, to produce finished viscose solutions by the processhereof of much lower or higher causticity and/or cellulose content.Again, it is possible to carry out the xanthating reaction attemperatures ranging from slightly above the freezing point to roomtemperature and to perform the treatment of the deaerated pulp chips atdistinctly sub-room temperatures down to the freezing point and withcaustic soda solutions of varying causticity, depending upon thecausticity to be realized in the finished xanthate solution. In otherwords, the causticity of the solution employed to form the pulpsuspension should such as to enable the realization of a xanthatesolution which immediately after the xanthating reaction or uponsubsequent dilution with water has the desired causticity in combinationwith the desired cellulose content. It is thus seen that the presentinvention, although involving the step of deaerating cellulose fibermore particularly in the form of pulpboard chips or sheet fragmentspreparatory to admixing caustic soda solution therewith to form a smoothpulp suspension, nevertheless lends itself to considerable variationinsofar as concerns other aspects, including the temperature,causticity, cellulose content, carbon bisulphide usage, etc., underwhich xanthation of the pulp suspension is effected. It might be notedthat while the step of deaeration is particularly valuable as applied topulpboard chips, sheet fragments, or other fiber aggregates offeringresistance to uniform impregnation and defiberization to form pulpsuspensions in caustic soda solution of the desired smoothness orfreedom from fiber aggregates, yet such step is also of value in formingsuch suspensions from cellulose fiber in other conditions, for instance,in shredded condition, as a deaerated mass of shedded cellulose fiber isalso more quickly and uniformly wet or soaked with caustic soda solutionand resolved into a smooth fiber suspension than when the solution mustfirst displace the air entrained throughout the mass.

I claim: 1. A process of making cellulose xanthate solutions involvingthe reaction of cellulose fiber, caustic soda solution, and liquidcarbon bisulphide, which comprises confining a mass of cellulose fiberin the form of pulpboard chips, sheet fragments, or other fiberaggregates in a closed mixing vessel, evacuating air from the vessel,mixing caustic soda solution with the mass in the evacuated vessel toeffect a substantially uniform impregnation and softening of the fiberaggregates with the solution and finally a disintegration of suchaggregates into a smooth fiber suspension substantially free fromaggregates in the caustic soda solution, and mixing liquid carbonbisulphide with the resulting fiber suspension until the fiber has beensubstantially completely xanthated and dissolved to yield a solution ofcellulose xanthate.

' 2. A process of making cellulose xanthate solutions involving themixture and reaction of cellulose fiber, caustic soda solution, andliquid carbon bisulphide in a single mixing vessel, which comprisesconfining in a closed mixing vessel a mass of cellulose fiber in theform of pulpboard chins of an area no greater than about one squareinch, of a thickness of about 0.030 to 0.060 inch, and of a compactnessof about 50 to 120, evacuating air from the vessel, mixing caustic sodasolution with the mass in the evacuated vessel to effect a substantiallyuniform impregnation and softening of the chips with the solution andfinally a disintegration of the chips into a smooth fiber suspensionsubstantially free from aggregates in the caustic soda solution, andmixing liquid carbon bisulphide with the resulting fiber suspension inthe vessel until the fiber has been substantially completely xanthatedand' dissolved to yield a solution of cellulose xanthate.

3. A process of making cellulose xanthate solutions involving themixture and reaction of cel-' lulose fiber, caustic soda solution, andliquid carbon bisulphide in a single mixing vessel, which comprisesconfining in a closed mixing vessel 9. mass of cellulose fiber in theform of pulpboard chips, evacuating air from the vessel, mixing causticsoda solution with the mass in the evacuated vessel to efiect asubstantially uniform impregnation and softening of the chips with thesolution and finally a disintegration of the chips into a smooth fibersuspension substantially free from aggregates in the caustic sodasolution, introducing nitrogen into the vessel above the resultingsuspension of fiber, and mixing liquid carbon bisulphide with theresulting fiber suspension in the vessel until the fiberhas beensubstantially completely xanthated and dissolved to yield a solution ofcellulose xanthate.

4. A process of making cellulose xanthate solutions involving themixture and reaction of cellulose fiber, caustic soda solution, andliquid carbon bisulphide in a single mixing vessel, which comprisesconfining in a closed mixing vessel 9. mass of cellulose fiber in theform of pulpboard chips, evacuating air from the vessel while heatingthe mass of chips therein to expel air and residual moisture from thechip interstices, mixing caustic soda solution with the mass in theevacuated vessel to effect a substantially uniform impregnation andsoftening of the chips with the solution and finally a disintegration ofthe chips into a smooth fiber suspension substantially free from fiberaggregates in the caustic soda solution, and mixing liquid carbonbisulphide with the resulting fiber suspension in the vessel until thefiber has been completely xanthated and dissolved to yield a solution ofcellulose xanthate.

GEORGE A. RICHTER.

